Dielectric gap miniaturized microwave filter



p 7, 1965 E. w. SEELEY ETAL 3,205,460

DIELECTRIC GAP MINIATURIZED MICROWAVE FILTER Filed Sept. 18, 1961 2 Sheets-Sheet 1 JOHN R. ALDAY ELWIN W. SEELEY INVENTORS.

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ATTORNEY P 1965 E. w. SEELEY ETAL 3,205,460

DIELECTRIC GAP MINIATURIZED MICROWAVE FILTER Filed Sept. 18, 1961 2 Sheets-Sheet 2 FREQUENCY RESPONSE CURVE DIELECTRICALLY LOADED MICROWAVE WAVEGUIDE BANDPASS FILTER INSERTION LOSS IN BANDPASS .4 DB

INSERTION LOSS DB 5 '23 I L .5 5.6 5.7 5.8 5.9 6.0 6.l KMC FREQUENCY KMC F IG. 3

JOHN R. ALDAY ELWIN W. SEELEY INVENTORS.

ATTORNEY United States Patent 3,205,460 DIELECTRIC GAP MINIATURIZED MIQROWAVE FILTER Elwin W. Seeley, Riverside, and John R. Alday, Corona, Caliii, assignors to the United States of America as represented by the Secretary of the Navy Filed Sept. 18, 1961, Ser. No. 139,010

3 Claims. (Cl. 333-73) (Granted under Titie 35, US. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to waveguide structures for microwaves and more particularly to a microwave waveguide filter for dielectrically loaded waveguides.

Various susceptances have been caused in a waveguide by means of inserting metal irises therein. However, metal machining of slots for irises and their assembly within a section of waveguide is complicated and requires that the waveguide be cut open; also, the size of the irises are very critical. The present invention performs the same function as metal irises, but the construction is greatly simplified, since a section of waveguide having a dielectric slab with air gaps along the length thereof is all that is necessary, and provides greater care in manufacturing than heretofore possible.

It is an object of the present invention to provide a new and improved microwave waveguide filter.

Another object of the invention is to provide a new and improved dielectrically loaded waveguide for rejecting frequencies above and below a given spectrum.

A further object of the invention is to provide a waveguide using a dielectric slab having gaps therein to determine the desired filtering characteristics.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic cross-sectional view, taken along line 1-1 of FIGURE 2, illustrating the principle of the invention applied to a waveguide section.

FIGURE 2 is a longitudinal sectional view of the invention, taken along line 22 of FIGURE 1.

FIGURE 3 shows a typical frequency response curve for a dielectrically loaded microwave waveguide bandpass filter of the present invention.

Referring now to the drawings like numerals refer to like parts in each of the figures. A section of waveguide having rectangular cross-section is provided with a slab 12 of alumina or other suitable dielectric material positioned centrally between the narrow sides of the waveguide, as shown in FIGURE 1, and running lengthwise along the length thereof. Portions of the slab are removed thus providing air gaps 14 between various sections of slab 12, as shown in FIGURE 2. One or more tuning screws 16 are provided for fine tuning of the waveguide filter.

'In the present type of filter, the length of the gaps 14 between sections of dielectric 12 forms the desired susceptances and the length of each section of dielectric 12 forms the desired spacing between the susceptive elements. By adjusting the gaps 14 and lengths of dielectric 12, a microwave filter of desired characteristics can be realized. The lengths of the dielectric slabs 12 in the filter determine its center frequency of operation; i.e., the longer the slabs the lower the center frequency. The lengths of the air gaps .14 determine the broadness of the passband of the filter; i.e., the greater the air gaps the nar- Patented Sept. 7, 1965 'ice rower the passband of the filter. The number of sections in the filter determine the sharpness of the passband. Each section consists of a slab 12 between two air gaps 14, as shown in FIG. 2. In other words, the frequency band through which the filter will operate is governed by the lengths of the dielectric slab sections and the air gaps. Fine tuning of the filter is provided by adjusting tuning screws 16.

In FIGURE 3 is shown a typical frequency response curve for a dielectrically loaded microwave waveguide bandpass filter, of the present invention, wherein the insertion loss in the bandpass is less than 0.4 decibel.

This filter is suited for use with dielectrically loaded waveguide microwave systems. The dielectric slab can be precut into sections of desired length and then inserted into a waveguide section for ease of construction.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A microwave waveguide filter comprising a section of waveguide having a rectangular cross-section, a slab of dielectric material positioned centrally between the two narrow sides of and entirely within said section of waveguide and running lengthwise along the length thereof, portions of said slab being removed to provide a plurality of separated sections of said slab and air gaps bet-ween said sections of said slab along the length of said section of waveguide, and at least one tuning screw in a broad side of said section of waveguide for fine tuning of said filter.

2. A microwave filter comprising a section of waveguide having a slab of dielectric material positioned centrally along the length and entirely confined within the walls thereof, portions of said slab of dielectric material being removed at desired intervals along the length thereof to provide a plurality of separated sections of said slab and to provide a plurality of air gaps of desired length between said sections of slab, the length of said gaps determining the susceptance for each section of the filter and the length of each separate section of slab forming the desired spacing between the susceptive elements, and at least one tuning screw in a broad side of said section of waveguide for fine tuning of said filter.

3. A microwave waveguide filter for dielectrically loaded waveguide comprising a section of rectangular waveguide, a plurality of separate rectangular sections of dielectric material spaced apart along the length and positioned centrally within and spaced from the narrow sides of said section of waveguide, each section of said dielectric material being in contact with the Wide sides of said section of waveguide, the length of the spaces between consecutive sections of said dielectric material being adjusted to determine the susceptances for each section of the filter, the length of each section of dielectric being the desired spacing between susceptive elements, and at least one tuning screw in a broad side of said section of waveguide for fine tuning of said filter.

References Cited by the Examiner UNITED STATES PATENTS 2,106,768 2/ 38 Southworth 333-73 2,546,742 3/51 Gutton 33373 2,697,209 12/54 Sichak 3 33-73 2,877,433 3/59 Devot 33373 2,938,177 5/60 Vogelman 333-9 HERMAN KARL SAALBACI-I, Primary Exiaminer. 

1. A MICROWAVE WAVEGUIDE FILTER COMPRISING A SECTION OF WAVEGUIDE HAVING A RECTANGULAR CROSS-SECTION, A SLAB OF DIELECTRIC MATERIAL POSITIONED CENTRALLY BETWEEN THE TWO NARROW SIDES OF AND ENTIRELY WITHIN SAID SECTION OF WAVEGUIDE AND RUNNING LENGTHWISE ALONG THE LENGTH THEREOF, PORTIONS OF SAID SLAB BEING REMOVED TO PROVIDE A PLURALITY OF SEPARATED SECTIONS OF SAID SLAB AND AIR GAPS BETWEEN SAID SECTIONS OF SAID SLAB ALONG THE LENGTH OF SAID SECTION OF WAVEGUIDE, AND AT LEAST ONE TUNING SCREW IN A BROAD SIDE OF SAID SECTION OF WAVEGUIDE FOR FINE TUNING OF SAID FILTER 